Could your seafood contain toxic chemicals?

— When you think of tainted seafood, you may think of the Gulf oil spill. But 80 percent of the fish and shrimp Americans eat actually comes from overseas — and a TODAY investigation that aired Tuesday found that some of that seafood may contain toxic chemicals that can cause serious health problems.

Footage taken by a U.S. advocacy group of seafood being raised in Vietnam, for example, showed fish in dirty sewage water, pumped with toxic antibiotics and banned drugs just to keep them alive, boosting production and driving down costs.

‘Disturbing number’Ron Sparks is commissioner of the state Department of Agriculture in Alabama — one of the few states that tests imported seafood for drugs like chloramphenicol, nitrofurans and malachite green, chemicals so toxic to humans that they’re banned in all food. “In some cases, between 40 and 50 percent of our tests will come out positive,” Sparks said. “That’s a disturbing number.”

State tests in Oklahoma, Mississippi and Georgia show similar results, all targeting seafood with the worst record of contamination: shrimp, catfish, crabmeat and tilapia imported to the U.S. from China, Taiwan, Vietnam, Malaysia and Indonesia — ending up in American restaurants and grocery stores in many cases, officials say.

“Unfortunately, consumers can’t tell if any of these compounds are in their seafood,” said Joe Basile, a seafood chemist for the Alabama Department of Agriculture. “You can’t smell it, can’t taste it, you can’t cook it out.”

Scientists say that over time, eating seafood contaminated with such chemicals could cause anemia, cancer and even birth defects.

The Food and Drug Administration says that the risks are long-term and not fully understood. While the FDA is responsible for keeping the nation’s food supply safe, TODAY’s investigation found that the FDA tests less than 2 percent of imported seafood.

“I would certainly suggest that the FDA do more,” Sparks said.

‘Cat-and-mouse game’Government tests show that U.S. seafood is free of these contaminants, but as far back as 2007, a congressional report found that “seafood imports remain especially problematic” and that the “FDA lacks sufficient resources and authority to ensure food safety.”

The FDA declined to speak with TODAY on camera, but said it is doing the best it can, targeting its testing on companies and countries that are repeat offenders and rejecting their products until they are proven safe. Yet the problem keeps happening: In fact, according to test results obtained by NBC News, this year alone 8 percent of the seafood the FDA tested from China was tainted, and 16 percent of seafood tested from Taiwan was tainted.

John Connelly, who runs a trade group representing the imported seafood industry, said, “Any unauthorized use of an antibiotic is inappropriate. The vast majority of seafood coming in does not exhibit any kind of problems.”

Connelly said most importers follow the rules, and that the problem is being overblown as a trade issue. “Unfortunately, there are bad actors in every industry,” he said.

Federal law requires grocery stores to identify the country of origin of the seafood they sell, but in restaurants, it's a different story: Most states do not require them to tell patrons where the seafood they serve comes from.

Connelly said that “studies do not indicate that Americans are deeply interested in the source of their fish or other proteins.

“I think that consumers should feel comfortable that the FDA does a good job,” he added.

But some officials say that until more seafood is tested, consumers are at risk. “It is a cat-and-mouse game,” Joe Basile said. “They quite honestly don’t care about the health of United States citizens.”

And officials say it is not just a health issue. American fishermen who play by the rules say they’re losing their jobs because they can't compete with importers who cut corners and sell their tainted fish much cheaper in the U.S.